The abbreviation mode in Emacs is called Abbrev-mode. With the correct configuration, you can write fyiSPC and “For your information” will be inserted in the buffer. This, in itself, is really sweet.
Unfortunately, you will soon face tough choices… how many words start with con? Or def? Define? Defer? Diesel Exhaust Fluid? If you are like me, after 10 or 20 words you will stop adding new abbreviation and forget about abbrev-mode. (But as I already said in another post, I’m really dumb.)
Recently I’ve re-started adding new abbreviations, but divided in semantical field. I guess you haven’t heard these words since high school! What’s so interesting in doing this, is that you don’t have to be sure your abbreviation won’t clash with another word. As I mostly write HVAC related words in my work, I have a file with abbreviations only for that. In this file, ac will be for air conditionning, fa for fresh air, fsp for furnace set point, and so on.
Depending of the context, you could write entire paragraphs with only half the written character! The productivity boost is staggering!